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On the basis of extensive experience already achieved in the field of quantum dots (QDs) we plan to develop the next generation of semiconductor lasers with performance superior to the present quantum well (QW) and quantum dot devices: lower threshold currents, higher temperature stability, extended emission range, large catastrophic optical damage threshold, low chirp operation. QD amplifiers with significantly improved performance as compared to the present devices will be also elaborated. To fulfil these tasks a growth technology to fabricate long wavelength (1.1-1.4 µm) QDs on GaAs substrates with controlled parameters (size, shape, emission wavelength, density, size distribution) is to be worked out. Structural properties of QDs and QD geometry will be evaluated and their electronic spectrum will be investigated using optical methods. QD lasers and amplifiers with a variety of QD arrays in the active medium and device designs will be grown and investigated. Extensive experimental studies and theoretical simulations of QD lasers and amplifiers will be performed to optimise their characteristics according to different criteria such as low threshold, high output power. As a result of this investigation a deep insight in the physics of QD lasers and amplifiers will be gained and devices with significantly improved performance will be developed. Description of the research activities. The QD arrays with controllable parameters will be grown by Molecular Beam Epitaxy and Metal Organic Chemical Vapour Deposition. Novel growth approaches such as alloy phase separation activated by small coherent islands, using of seed layers composed of QDs or QD stacks, temperature ramping during QD formation, QD deposition using alternating beams of In, As4, Ga, and Al, deposition of InAs and GaAs monolayers on top of QDs as well as combinations of these approaches will be explored. Besides, new approaches will be developed. Special in-situ overgrowth/annealing techniques will be applied to eliminate dislocations and defects in QD arrays.

The actual parameters of QDs (size, shape, electronic structure) will be determined by Transmission Electron Microscopy as well as by optical methods: photoluminescence (PL), time-resolved PL, PL excitation spectroscopy. Capture/escape and relaxation/excitation rate constants will be calculates with the use of QD electron and hole wave functions computed by extended 8-band kp method. Main characteristics of QD lasers and amplifiers will be simulated using rate equations for populations of QD carrier levels in homogeneously broadened QD ensemble and Maxwell equations for electromagnetic field. Devices optimised for diverse applications (particularly high power applications) will be designed. Sets of QD lasers and amplifiers with distinct QD arrays in the active medium and device designs including theoretically calculated structures will be grown. Their threshold currents, differential efficiencies, gain-current and light-power characteristics, near- and far-fields, lifetime, dynamic properties will be investigated. The results obtained will be used to improve theoretical models and to perform optimisation of the device characteristics.Expected results. QD structures with required parameters of an individual QD (lateral size, height and correspondingly position of energy levels) as well parameters of the whole QD array (density and size distribution). Realistic theoretical model, describing main characteristics of QD lasers and amplifiers. Deep understanding of the influence of the parameters of QD array and device design on characteristics of lasers and amplifiers. QD lasers with controllable wavelength (in particular 1120 nm, 1300 nm), high output power (> 1 W single mode, continuous wave), high temperature stability (T0> 200K), and lifetime more than 1000 hours at 60oC. QD amplifiers with faster gain compression recovery and reduced carrier heating for both gain and refractive index dynamics as compared to bulk and QW devices.